The purpose of this investigation is to establish, at the molecular level, the basis of the acquisition of gluocorticoid resistance in the glucocorticoid-sensitive human leukemic T-cell lline CEM-C7. Using various techniques of cell biology, biochemistry, somatic cell genetics and immunology we will examine in normal and variant cell lines whether abnormalities in receptor function result from alterations within the receptor protein itself or whether these abnormalities result from alterations in factors which may moderate receptor function. Using classical techniques of steroid-receptor biochemistry, as well as newly derived specific antireceptor antibodies and covalent steroid affinity labels, receptors from steroid-resistant variants containing no apparent steroid binding activity or containing receptors defective in activation will be analyzed and compared by a variety of physical techniques to the normal receptors of the senstive parent. Somatic cell hybrids between these classes of resistant cells will be constructed to determine i) whether these two phenotypes are dominant or recessive and ii) whether they are capable of genetic complementation. By defining, at a level of sophistication heretofore not achievable the properties of glucocorticoid receptors in steroid-resistant variants, the role of steroid receptors as regulators of gene expression can be explored in new depth. A clear understanding of the mechanisms of acquisition of steroid resistance in a model human cell line would provide the foundation for similar studies in steroid-resistant leukemias, and might eventually allow the determination of when steroid treatment of certain leukemias will be useful and when, if not useful, such treatment and its concomitant side effects would best be withheld.